The invention relates to a method for processing signals and to a circuit arrangement.
A method for processing signals which correspond to reflected waves which are transmitted or interrupted by a structure in order to be able to gather information and analyze the structure of this material is described in EP 0 825 453 B1. With the method described, the fact that every point of an object to be examined leads to a reflected wave which is then stored at positions of the storage unit which are distributed in the form of parabolic curves, the characteristics of which depend on the distance of the point relative to the probe and on the radiation pattern of each element. In the known method, a probe is used which is configured linearly and composed of a plurality of transmitter/receiver elements of small dimensions. The same probe is then used for transmission and reception. First, a wave front is transmitted into the object to be examined and those waves which are reflected by the structure are received.
The information which is emitted by the sensor elements is then digitalized and stored and, more particularly, is stored in a storage element which has a line for each sensor element.
Subsequently, the structure of the object is reconstructed and/or analyzed with reference to the information that was stored in the storage elements. For each point of the object the position of the storage element is computed which contains the signals which are located by the sensor elements and correspond to the waves reflected or transmitted from this point. This position is computed with aid of an addressing rule whose parameters depend on the position of this point in relation to the sensor elements. Furthermore, the lines of the field storage are read for each point at the respective positions which were previously computed for this point, a mathematical operation being used for the values read for this point in order to obtain a result which is representative for the range of the wave. For the computation, all cells of the storage field are read in parallel for this point at the positions which are designated for this point in the respective allocated addressed storage units.
Since the computation of each reading principle for reading out the storage would take too long to effect in real time, this computation is done in advance and the results stored in specific “address storage units” which are allocated to each line of the “field storage unit”.
Hence, it follows that the described method is only suitable for identifying specific, i.e. previously defined structures. After performing the mathematical operation, the contents of the field storage unit are stored in image storage unit, location and propagation time information being taken into consideration. In the method, computed B images are evaluated, as is common, for example, in medical diagnostics. However, for automatic material examination, B images should not be referred to since long evaluation times are required for the evaluation.
Furthermore, it should be noted that there are limits in defect detection with vertical acoustic irradiation since only one defective position can be detected. Furthermore, uncertainties occur in the defect evaluation, since fixed geometric relations between the probe and the test piece are a prerequisite, since location information is required for the defect determination. Therefore, the known method is very sensitive to conventional misalignments of the probe.